It’s an unusual reason to delay a cargo launch planned to dock with the International Space Station: moldy food bars.

Forty mice were going to hitch a ride today on board SpaceX’s latest cargo mission as part of a NASA-sponsored experiment called Rodent Research-8, which will explore mechanisms behind aging and age-related diseases.

But now they’ll have to wait until tomorrow to make their way to the ISS.

When technicians inspected the cargo on board SpaceX’s Dragon capsule before the scheduled launch, they found the mice’s food bars were covered in mold – not exactly the kind of organism the ISS usually likes to welcome aboard, especially given the recent news of antibiotic-resistant bacteria found on the space station.

And there’s another experiment that might be jeopardized thanks to the delay.

Scientists from Exeter, Nottingham and Lancaster universities in the UK had been planning to fly colonies of worms to the ISS to investigate the mechanisms behind muscle atrophy.

But thanks to the delay, the main colonies might already be “too old” for the experiment according to a report by the BBC.

But luckily, SpaceX only had to delay the launch by one day. Now it’s planning to launch tomorrow, December 5.

The weather conditions are looking good, so things are looking up for a successful launch.

It will take two days to reach the ISS, and the capsule will stay docked for a whole month.